There have hitherto been proposed a variety of optical tracing devices for reproducing a workpiece of a desired shape by optically tracing a contour of a given shaped templet.
As an optical tracing device, a scanning type tracer, in most cases, has been used for performing a tracing operation.
Usually, a circumferential portion of the templet is circularly scanned by the scanning rays of light radiated from a light source rotating at a given rate, and the scanning rays of light are reflected on the surface of the templet or transmitted through the templet, thus being received by the sensing head. The scanning rays of light thus received are converted by a converter to electric signals, for example, voltage, proportional to the intensity of the scanning light. The voltage thus converted is compared with a predetermined reference voltage, so that a difference between both voltage levels will be negatively fed back to servo-motors. The templet and the workpiece to be reproduced will be shifted by the servo-motors, while tracing the contour of the templet. This is because in the optical tracing device of this type, the intensity of the scanning rays of light received by the sensing head, i.e., analogue signals, is used as tracing signals necessary for tracing the contour of the templet. However, the optical tracing device has been susceptible to external conditions, with the failure of exact tracing of the contour of the templet used. A tracing device of the prior art requires servo-motors for effecting a tracing operation, resulting in the complexity in construction, as well as requiring an expensive servo-controlling system and other mechanisms associated therewith.